Chemical transfer receiving sheets and a method of preparing such sheets



3,518,160 CHEMICAL TRANSFER RECEIVING SHEETS AND A METHOD OF PREPARING SUCH SHEETS Dorothy J. Beavers and Henry C. Yutzy, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Continuation of application Ser. No. 293,882, July 9, 1963. This application Feb. 16, 1968, Ser. No. 706,192

Int. Cl. D21d 3/00 US. Cl. 162-135 6 Claims ABSTRACT OF THE DISCLOSURE A nucleated receiving sheet when used in a diffusion transfer process comprises a paper support which has impregnated therein a size comprising a hydrophilic colloid and silver precipitating nuclei. The size also preferably contains an antistain agent. Advantageously the size is applied as a tub size to the paper, and is impregnated therein by means of a size press roll.

This application is a continuation of Beavers and Yutzy U.S. application Ser. 'No. 293,882 filed July 9, 1963, and now abandoned.

This invention concerns nucleated receiving sheets for used in the photographic chemical transfer system and a method of preparing such sheets.

In the photographic chemical transfer system a positive image is obtained from the exposed silver halide emulsion by the diffusion of silver halide from the unexposed areas of the emulsion to a nucleated receiving sheet, wherein the nuclei form sites for the formation of a positive image.

In the actual operation of this system there are some areas which have required improvement. One of these has been the need for an improved receiving sheet, since many of the receiving sheets commonly available have been subject to curling, staining and the like. Moreover, it has been desirable to control the quality of the positive image.

Nucleated receiving sheets are customarily made by a surface coating of nuclei contained in a binder, such as gelatin, car-boxymethylcellulose or the like. The nuclei are precipitated in an amount of about 0.1 N to 0.0001 N and these nuclei coated at concentrations in the range of one milligram per square foot or less.

Normally, the paper is only coated on one side resulting in curl when the surface coating is dried, particularly at low relative humidities. In carrying out the chemical transfer process, extreme care must be taken to obtain good contact between the surface of the receiving sheet and that of the silver halide emulsion, in order that the image areas will be distinct, with good sharpness and con trast. In addition, if the chemical transfer is carried out in a darkroom, it has been somewhat difficult to tell which side of the paper contained the nucleated coating, and it has been preferred to have a receiving sheet with either side usable. Also, since a yellow hydroquinone stain has often appeared on the receiving sheet, a means of avoiding this stain has been sought.

Attempts made to prepare a nucleated paper by other means have sometimes resulted in unsatisfactory results evident in the receiving sheet. For instance, using a nuclei suspension as a tub size of the same concentration as that used for a surface coating results in decreased print densities of only 0.10 to 0.20. Moreover, adding nuclei to a gelatin size normally used as a tub size results in mottle.

United States Patent We have found a method of tub sizing receiving sheets which provide good image differentiation without stain, mottle or detrimental curl.

One object of this invention is to provide a nucleated receiving sheet paper with reduced curl. Another object is to provide a receiving sheet paper for use in the photographic chemical transfer process by immersing the freshly made paper web through at least one sizing bath and then passing it through press rolls to force the sizing into the stock and to remove the excess from the surface. An additional object is to provide a method for preparing nuclei-containing paper so that the paper will withstand wide variations in relative humidity without any appreciable curl. A further object is to provide a method of obtaining a receiving sheet in which either or both sides may be used to form the positive print. A still further object is to provide a method for obtaining a positive image in the photographic chemical transfer process having improved photographic characteristics and relatively free from stain and mottle.

The above objects are obtained by applying the antistain agent and the nuclei as a size press coating. The paper is preferably first immersed in a bath containing the antistain agent and nuclei and then passed through a second size containing nuclei. This method is particularly applicable to a Fourdrinier sheet which, while not exhibiting poor curl when freshly coated with a surface coating, shows bad curl after the coated paper is four to six months old. In addition, the Fourdrinier sheet normally shows bad curl away from the gelatin coating, no matter which side (face or wire) the coating is on. A cylinder papermaking machine sheet or a pressure Fourdrinier sheet usually exhibits a bad curl only when the gelatin coating is applied on the wire side.

The paper coming off the paperrnaking machine is tub sized and while still wet is passed under a size press roll to force the antistain agent and nuclei into the stock and to remove the excess from the surface, after which it is dried.

We have found that the antistain agent is preferably a slightly soluble or water insoluble acid such as boric, phthalic, benzoic, adipic, etc., or ammonium salts of more water soluble acids. Solvents for these acids may be used to incorporate the acids into the raw paper stock, but it is preferable to add the acids to the nuclei gel size as slurries, dispersions, or hot solutions. The amount of antistain agent will depend upon the paper thickness but is preferably within the amount of 0025-12 grams per square foot.

In some applications, the use of low solubility organic acids presents a problem as to method of application, for instance, where it is not desirable to use organic solvents in the surface sizing solution. A further restriction on the use of low solubility acids is the maximum solution temperature of about 120 P. which must be observed because of safety considerations in threading paper through the hot sizing solution.

It has been found that, when an organic acid (such as phthalic acid) has borderline solubility at the desired temperature and concentration, the addition of a small amount of another organic acid (such as benzoic acid) of lower solubility will result in a combined solubility which is greater than either acid separately. This makes possible the use of low solubility organic acids from water solution Without requiring high temperatures.

Thus a mixture of 82.5% phthalic acid and 17.5% benzoic acid can be dissolved (and remain dissolved) at 3% solids in water at temperatures of -120 F. This cannot be done with either acid separately. The nuclei, which may be conventional nuclei types, such as colloidal metals or metal sulfides, e.g. colloidal silver,

3 silver and zinc sulfides or various nuclei mixtures, may be applied within the range of 0.1 to 50 milligrams per square foot for the first size bath. These nuclei pref-- erably have an average diameter of about 25 to 2,500 A.

In the second size bath no antistain agent is used, but only nuclei and a binder. The concentration of the nuclei is such that an amount within the range of 0.1 to 75 milligrams per square foot is applied on the paper stock. These quantities may be varied, but the total coverage is preferably within the range of 1 to mg/ft. but may be 0.1 to 100 mg./ft.

It will be appreciated that the concentration of nuclei and antistain agent while within the range of 2.5 percent to 4.0 Weight percent for antistain agent in the first bath and 0.003 to 0.08 N nuclei will depend upon the speed with which the paper is passed through the size bath, the type of paper used, the amount of binder, the solvent, if any other than water, etc. Therefore, the coverage values are expressed herein in terms of final coating composition on a dry basis.

The paper base should be tub sized with solutions more concentrated than the normal gelatin size of two or four percent. Best results are obtained with gelatin solutions of six percent or more, preferably about ten percent. Higher concentrations of gel can be used but difficulty may be experienced in drying these tub sized sheets on a papermaking machine. Two tub sizes are better than one tub size since the paper base has a smoother surface and gives prints with little or no mottle. Tub sizes lower than six percent gelatin on rough surfaced cheap paper bases may give mottled prints. On the other hand, water finished stocks and clay or baryta coated stocks with their smooth surfaces give good densities upon tub sizing with lower nuclei-gel concentrations since the nuclei are retained at the surface.

After coating the paper with the press size coatings, the paper is passed through calender rolls wherein an extremely smooth surface is obtained. Various known methods of improving this surface during the calendering operation can also be applied at this time, such as calendering with heated rolls before the paper has been completely dried, applying moisture to the rolls in the form of steam or water during the calendering operation and the like. A useful embodiment of our invention is to water finish unnucleated paper stock at the calender stack with a dispersion of nuclei in gelatin to obtain a nucleated sheet.

In our preferred embodiment, the receiving sheet contains about 1 g./ft. gelatin with about 1-10 milligrams/ ft. zinc sulfide nuclei and about 0.10 g./ft. benzoic acid.

The concentration of a single size bath is preferably the same as that of the first size bath used in the twotub system except that the nuclei concentration is higher, being about 0.01 to 0.08 N. In some instances where a relatively smooth paper is used, or one which is clay or baryta coated, a single size bath may be sufiicient to obtain satisfactory results, although the two-bath system is preferred for most purposes.

The gelatin coverage of the receiving sheet prepared by our process preferably has a range of 0.2 to 3.0 grams per square foot.

Although gelatin is our preferred binder in the tub sizes, other colloidal materials which are similar may be used, for example, such as the well-known proteins, casein, zein, and the like, polyvinyl alcohol, polyvinyl acetate, acrylic polymers and the like.

The amounts of other binders used in place of gelatin or in conjunction with gelatin depends upon the viscosity of the dispersion. For-example, When polyvinyl acetate is used as the binder, -45 percent of the dispersion can be polyvinyl acetate depending upon the resulting viscosity. If a solvent is used for the polyvinyl acetate, a lower concentration might be used in the size bath. A preferred coverage on the paper base is 0.5-6.0 g./ft.

.solids basis. A useful embodiment comprises a tub size coating of polyvinyl acetate or a similar water resistant compound alone under the nuclei coating as an antistain agent.

It will be appreciated that receiving sheets using this method can be prepared incorporating a mordant for use with color processes especially incorporating an acid and a mordant for use with color transfer processes such as those described in British Pat. 840,731. Paper or other supports for use with a wash-off solvent transfer element can also be prepared by tub sizing. For example, the mordant material and/or acid can be incorporated in a gelatin tub size as the paper comes off the paper machine. It can be added to the support particularly if it is of some other material than paper as a tub size after the support has been formed. For use in the wash-off solvent transfer system, the support is tub sized with the nuclei and/or antistain agent prior to coating thereon the photographic emulsion which is washed off after developing, to disclose the image which is left in the nucleated support.

The following examples are intended to illustrate our invention but not to limit it in any way.

EXAMPLE 1 Preparation of 0.02 N ZnS nuclei, 12% gel (6 liter batch) To the kettle at 40 C., add 2880 g. 25 percent gelatin solution, 1270 ml. H O, a solution of 318 g. sodium thiosulfate (5H O), 15 g. sodium sulfite and 12 ml. of gel preservative. Dissolve and add ml. of 1.0 N sodium sulfide and stir three minutes. A solution of ml. zinc nitrate (1.0 N) is diluted to 1580 ml. with water and this solution is added to the kettle in 5 minutes at 40 C. This nuclei gel melt is used as a tub size. An antistain agent may be added, and if desired, nuclei cold toners.

EXAMPLE 2 Tub sizes containing acids or ammonium salts of acids for antistain protection The following were used as first tub sizes:

(A) To 300 g. of 0.02 N ZnS nuclei (12% gel) melted at 50 C. is added a solution of 85 g. phthalic acid in 500 ml. methanol over a 5 minute period. This turbid solution used as the antistain first tub adds about 0.6 g./ft. of solids to non-tubbed sized stock.

(B) 3000 g. 0.02 N ZnS nuclei (12% gel) melted at 50 C. is added to a solution of 102 g. boric acid in 400 ml. water.

(C) To 2325 ml. H O at 5060 F. is added 75 g. phthalic acid. When the acid is dissolved, 600 g. gelnuclei mixture is added prepared according to Example 1.

(D) To 0.02 N ZnS, (10% gel) add 4 percent ammonium acetate or ammonium borate and dissolve.

Second tub size.--To 6000 g. of 0.02 N ZnS nuclei in a 10 to 12 percent gel melt was added a solution of cold toning agent. This solution is used as a second tub size. Using the first tub sizes described in Example 2 plus the second tub sizing described above adds about 0.9 to 1.1 g./ft. of solids to non-tubbed sized paper. Excellent non-yellowing two-sided chemical transfer positive prints are obtained when an exposed silver chlorobromide emulsion is processed with a silver halide developer in the presence of a silver halide solvent.

EXAMPLE 3 A nucleating solution of 0.0012 N silver sulfide in 12 percent paper mill glue-gel size was prepared essentially as in Example 1, except that silver nitrate was used rather than zinc nitrate. To 300 g. of this nuclei solution was added a solution of cold toner and this solution used as an 11 percent gel-glue tub size on non-tubbed sized stock, water finished stock and baryta coated stocks.

Excellent high density positives were obtained on the smooth surfaced, water finished and baryta coated stocks.

EXAMPLE 4 A tub-sized nucleated-acid-treated receiving sheet was prepared by passing a paper support through two consecutive tubs containing the following ingredients.

First tubA 12 percent gelatin solution containing 3500 grams of water, 85 grams of phthalic acid and 0.02 N zinc sulfide.

Second tub--A 12 percent gelatin solution containing 0.02 N zinc sulfide.

A second nucleated receiving sheet was prepared by surface coating a gel sized paper support on both sides with a 7 percent gelatin solution containing 0.02 N zinc sulfide.

A negative sheet was prepared by coating a paper support with a silver chloride emulsion at a coverage of 90 milligrams of silver and 220 milligrams of gelatir; per square foot. Over the emulsion layer, there was coated a layer of carboxymethyl cellulose at a coverage'of 100 milligrams per square foot.

The negative was exposed to a line subject and bathed in a diffusion transfer developer of the type described in Example 4 of US. Pat. 2,987,396. During development, the exposed negative sheet was squeegeed in contact with the tub-sized receiving sheet described above for 10 seconds and the two sheets then separated. A similar exposed negative was squeegeed in contact with the receiving sheet having the nuclei coated on the surface. After a 10 second transfer time, this sheet produced an image having considerably lower D and poorer quality than when the tub-sized nucleated receiving sheet was used.

EXAMPLE 5 A nuclei tub size was prepared in the manner described in Example 1 containing 0.01 N silver sulfide with 14.5 percent bone gelatin tub sizes. When used as a tub sizing solution, with or without antistain agents in the first tub, excellent high density positives were obtained. A dispersion of 40 percent polyvinyl acetate may be used as an antistain agent in the first tub alone, or with a gel nuclei mixture, with two 0.01 N Ag S, 14 percent gelatin sizes. These nucleated, sized, antistain positive Chemical Transfer papers will process satisfactorily in a Chemical Transfer Developer containing at least more than 5 g./l. of hydroquinone. A developer containing 6 g./l. of hypo gives Chemical Transfer positives with a cleaner background than developers without hypo. If desired, compounds, such as mercaptans, which give blacker images, can be incorporated in the nuclei size, in the negative sheet or in the processing solution.

It will be appreciated that our preferred embodiment involves tub-sizing the incompletely dried paper as it comes off the paper machine prior to calendering. However, the tub-sizing technique may also be used advantageously with paper which has already passed through the calendering operation such as paper commercially available, including well known papers such as Water finished, clay filled, baryta coated and the like.

EXAMPLE 6 The use of nucleated gel sized paper in a wash-off solvent transfer system A sized, nucleated sheet was prepared on a tub-sizing machine in the following manner. The first tub contained 0.02 N ZnS, 12 percent gelatin and hypo while the second tub contained, in addition, an appropriate cold toner. This nucleated, sized sheet was overcoated with an interlayer of 0.02 g./ft. of ethyl cellulose phthalate to facilitate the wash-off of the silver chlorobromide emulsion-ethyl cellulose phthalate layer which was coated over the interlayer.

A sample of the above coating was exposed on an Eastman 1B sensitimeter and then processed for one minute in a developer of the type described in US. Pat. 2,685,514 to Haist et al., at 71 F. After processing, the strip was washed to reveal a positive image with a D of 1.07 with a slight background density.

EXAMPLE '7 Sized, nucleated chemical transfer sheets used as receiver sheets in a normal solvent-dilfusion transfer system A nucleated, sized receiver sheet prepared as described in Example 6 and a similar sheet which contained, in addition, an antistain agent were used as receiver sheets in a solvent-diffusion transfer system.

A coated sample of a high speed silver bromoiodide emulsion was exposed on an Eastman IB sensitometer with an appropriate filter for 14 second. The exposed sample was then processed by attaching a pod containing a viscous solvent silver halide developer between the exposed negative element and the respective receiver sheet and passing them, in sandwich form, between two rollers. After processing times of 10 seconds and 20 seconds, the negative was stripped from the receiving sheet and the positive image thereon was stabilized. All of the positive images were found to have a sharp, dark brown image of very high quality and density. A high density, cold-black image would be obtained in place of the brown image by the incorporation of an appropriate cold toner in the system.

EXAMPLE 8:

A mordant gel sized sheet used as a receiver in color transfer processes British Pat. 840,731 was exposed through a color correction filter. The element and the gel-mordant sized receiver sheet were dipped into a developer as described on page 5 of British Pat. 840,731 for 30 seconds and then rolled together on a constant temperature plate held at F. After 5 minutes, the sheets were separated and the positive image containing receiver sheet was washed in cold water for 5 minutes. The positive color transfer image was of good quality. Other mordants, e.g. long chain quaternary salts, were used at various mordant to gel size ratios and produced color transfer images of similar quality. It was found that lower minimum density in the prints was obtained by using gelatin alone in the first sizing tub and gelatin plus a suitable mordant in the second sizing tub. A non-mordant cotaining gel sized paper base produced a weak positive color transfer image with poor color reproduction.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. A nucleated receiver sheet for use in a diffusion transfer process comprising a paper support impregnated with a size comprising a hydrophilic colloid, silver precipitating nuclei and an anti-stain agent, said size comprising about 0.2 to about 3.0 g. of colloid per square foot, about 0.1 to about 50 milligrams per square foot of nuclei and about 0.025 to about 1.2 g./ft. of antistain agent.

2. A process for providing a nucleated receiving sheet for use in a dilfusion transfer process comprising impregnating a paper sheet after forming on a papermaking machine with a size comprising a hydrophilic colloid, silver precipitating nuclei and an anti-stain agent after which said sheet, while still wet, is passed under a size press roll to force said size into said sheet and remove any excess size from said sheet, said size having been impregnated in an amount of about 0.2 to about 3.0 g./ft. of colloid, about 0.1 to about 50 mg./ft. of nuclei and about 0.025 to about 1.2 g./ft. of support.

3. A process for providing a nucleated receiving sheet for use in a diffusion transfer process comprising (1) impregnating an incompleted dried paper sheet, after forming on a papermaking machine, with a size containing colloid, nuclei and anti-stain agent in an amount of about 0.2 to about 3.0 grams per square foot of colloid, about 0.1 to about 50 milligrams per square foot of nuclei and about 0.025 to about 1.2 grams per square foot of an anti-stain agent, (2) passing said sheet under a size press roll, (3) impregnating said sheet with a colloid size containing nuclei in an amount of about 0.1 to about 75 milligrams per square foot nuclei and about 0.2 to about 3.0 grams per square foot of colloid and, (4) passing said sheet under a size press roll.

4. A process of claim 3 in which said nucleated receiving sheet is subsequently surface coated with a silver halide photographic emulsion.

5. A process of claim 3 in which said anti-stain agent is an organic acid.

6. A process of claim 3 in which said colloid is gelatin and said nuclei are silver sulfide.

References Cited UNITED STATES PATENTS OTHER REFERENCES Casey, Pulp and Paper, vol H, 2nd Edition, 1960, Interscience Publisher Inc., NY. page 1118.

S. LEON BASHORE, Primary Examiner T. G. SCAVONE, Assistant Examiner US. Cl. X.R. 

